It is well known that human perception of the brightness of a stimulus is significantly affected by the relative luminance of the background. This is illustrated in the familiar optical illusion of comparing a gray square surrounded by black to another gray square of the same darkness level surrounded by white. The gray square surrounded by white will appear darker than the one surrounded by black.
This same problem exists in the field of video and similar displays, for instance large screen televisions, movie theaters using electronic displays, etc. See “Considering the Surround in Device-Independent Color Imaging”, Mark D. Fairchild, Color Research and Application, Vol. 20, p. 352-363 (1995) incorporated by reference herein. This points out that changes in the surround of a video display effect the perception of the display. In other words, it is known that the relative luminance of the surround has an impact on the apparent contrast of the image on the display.